DESCRIPTION: (Applicant's Description) New and exciting advances have been made in the delineation of 1) genetic alterations which predispose to and/or cause breast and prostate cancer, 2) novel molecular mechanisms of hormone action, such as delineation of steroid receptor co-regulators, identification of novel steroid receptors, steroid hormone receptor interactions with membrane initiated signal transduction pathways, 3) identification of environmental hormone mimetics and novel mechanisms by which they may impact on growth and function of normal and cancerous breast and prostate. Since the growth and function of both normal breast and prostate are hormone dependent and their respective cancers are hormone responsive, delineating the roles and mechanisms of action of hormones is pivotal for progress in cancer etiology, prevention and therapy. Breast cancer and prostate cancer share many features: they are the most commonly diagnosed cancers in American women and men, respectively; both are regulated by sex steroids; both develop hormone independence; both have a hereditary component; both organs have a tubuloalveolar architecture; and for both organs, stromal-epithelial interactions play an important role in tissue morphogenesis and growth control. The goal of the proposed Keystone Symposium on Breast and Prostate Cancer is to provide a multidisciplinary program that addresses key questions and presents novel information about: 1) what are the mechanisms of action of endogenous hormones/growth factors and the role of exogenous hormones (hormone replacement therapy and/or environmental hormones) in etiology and progression of cancer 2) what is the interaction between hormones and gene mutations in carcinogenesis and 3) how can this knowledge be exploited to develop novel strategies for cancer prevention and therapy. It is expected that the knowledge shared and ideas generated will identify new directions for future endeavors and that bringing together researchers working on prostate and breast will have a synergistic impact on breast and prostate cancer.